Line coding is normally used to match the characteristics of a signal that is to be transmitted with characteristics of a channel over which the signal will be transmitted, e.g. to limit the DC contents of the signal and/or to facilitate clock recovery. Examples of line coding methods well known in the prior art are: Return to zero, NRZI non-return to zero invert on ones, Manchester encoding, Bi-Phase Mark, 3B/4B, 4B/5B, 5B/6B and 8B/10B, done in groups of bits before serialization.
U.S. Pat. No. 4,486,739 granted to Franaszek et al (that is incorporated by reference herein in its entirety) discloses an 8B/10B coder that is partitioned into a 5B/6B coder which encodes a 5 bit nibble, and a 3B/4B coder which encodes a 3 bit nibble. The 5 bit nibble is encoded to 6 bits and the 3 bit nibble is encoded to 4 bits. U.S. Pat. No. 4,486,739 states that it is desirable to encode 8 bits at a time in code words of 10 bits to be transmitted, rather than 4 into 5. However, according to U.S. Pat. No. 4,486,739 a nonlinear encoding of eight bits presents difficulties in implementation, as well as the likelihood that a single error in detection will result in eight erroneously decoded data bits.
These problems are solved via the partitioned block format described in U.S. Pat. No. 4,486,739: that is, the eight bits are encoded using coders producing less than 10 bit outputs. These coders interact so as to yield the desired code words. U.S. Pat. No. 4,486,739 describes the result as a coder whose coding rate, complexity and error propagation are near the theoretical limits, and which has ancillary benefits in flexibility of adaptation to various situations. Other partitions beside the 5/6, 3/4 were considered by the inventors of U.S. Pat. No. 4,486,739, but all were deemed to have disadvantages in error propagation and other criteria.
U.S. Pat. No. 4,486,739 also states that single errors or short error bursts in the encoded line digits of any block code can generate a longer error burst in the decoded message. For the 8B/10B code proposed in U.S. Pat. No. 4,486,739 the effects of line digit errors are always confined to the 6B or 4B sub-blocks in which they occur and generate error bursts no longer than 5 or 3, respectively, from a single line digit error. This derives from the fact, that each 6B or 4B sub-block is uniquely decodable on the basis of just the values belonging to that sub-block and without any reference to disparity or other extraneous parameters. See also an article by Widmer AX and Franaszek PA, entitled “A DC-balanced, partioned block, 8B/10B transmission code,” IBM Journal of Research and Development, Vol. 27, no. 5, pp. 440–451, September, 1983 that is incorporated by reference herein in its entirety.
The above-described 8B/10B encoder can be used to encode signals that are generated by a Reed Solomon encoder as described in U.S. Pat. No. 5,687,181 granted to Suemura et al (that is incorporated by reference herein in its entirety). Specifically, U.S. Pat. No. 5,687,181 discloses in its FIG. 7 that a 64 bit parallel signal is divided into two parallel digital signals each of 8 byte width, with each byte being composed of 4 bits. The divided signals are inputted to two encoders for error correcting code. In the encoders, the parallel signal is encoded into a one byte error correcting Reed Solomon code wherein byte length is of 4 bits and code length is of 10 bytes.
According to U.S. Pat. No. 5,687,181, the parallel signal having 10 bytes in width outputted from the encoders is distributed with one byte in width being present in every ten transmitters by an interleaver. One byte is composed of 4 bits so that, in each transmitter, a signal having 4 bits in width is distributed from each of two encoders, and a parallel signal having a total of 8 bits in width is inputted. The transmitter comprises an 8B10B encoder, a parallel/serial converter and an optical transmitter. The parallel signal having 8 bits in width inputted thereto is encoded into 8B10B code and is converted into a parallel signal having 10 bits in width, which is then time-division multiplexed for transmission as one serial optical signal.
The following prior art references also provide background, and each of these prior art references is incorporated by reference herein in its entirety:
[1] Carrier sense multiple access with collision detection (CSMA/CD) access method and physical layer specifications, pp 927–940, IEEE Std 802.3, 1998 Edition
[2] Shu Lin, D. J. Costello Jr. Error Control Coding: Fundamentals and Applications, pp 29–33, 1983, Prentice-Hall
[3] S. B. Wilson, S. B. Wicker and V. K. Bhargava, Reed-Solomon Codes and Their Application, 1994, IEEE Press.
[4] C. Benz, M. Gowan and K. Springer. An Error Correcting Encoder and Decoder for a 1 Gbit/s Fiber Optic Link. Proc. IEEE 1991 Custom Integrated Circuits Conference, 7.1.1–7.1.4, San Diego, May 1991.
[5] K. Springer. A Forward Error Correcting Code for Gigabit Fiber Optic Links. Proc. SPIE—Int. Soc. Opt. Eng. (USA), vol. 1577, 1992, pp. 246–253. Conference on High-Speed Fiber Networks and Channels (1991), Boston, September 1991.